1. Field of the Invention
The invention relates to solenoid valves that control the pressure of hydraulic fluid, and manufacturing methods of the same.
2. Description of the Related Art
Conventionally, solenoid valves are known in the art which include a solenoid portion that generates an electro-magnetic force, a cylindrical sleeve having a valve hole, and a shaft-shaped spool valve that moves in the axial direction in the valve hole, and which controls the pressure of hydraulic fluid by the axial movement of the spool valve. See, e.g., Japanese Patent Application Publication No. 2012-220013 (JP 2012-220013 A).
The solenoid valve described in JP 2012-220013 A includes a linear solenoid that generates an electro-magnetic force, a sleeve having internal threads formed on the inner periphery of its one axial end, a spool valve that is pressed by actuation of the linear solenoid to move in the valve hole of the sleeve, a spring that biases the spool valve toward the linear solenoid, and an adjuster screw having external threads formed in the outer periphery thereof.
The adjuster screw has a function to adjust the biasing force of the spring. When attaching the adjuster screw, the external threads of the adjuster screw are made to mate with the internal threads of the sleeve to adjust the axial position of the adjuster screw, whereby the biasing force of the spring is adjusted.
First, the axial position of the adjuster screw is adjusted temporarily. Then, the sleeve is swaged from its outer periphery to fix the adjuster screw temporarily. This temporary fixing reduces the gap between the external threads of the adjuster screw and the internal threads of the sleeve, and suppresses wobbling of the adjuster screw in the axial direction. After this temporary fixing, the axial position of the adjuster screw is adjusted again as final adjustment, and further swaging is performed to fix the adjuster screw as final fixing. This suppresses fluctuation in spring load after adjustment, whereby the biasing force of the spring can be accurately adjusted.
The method for fixing the adjuster screw as described in JP 2012-220013 A suppresses axial movement of the adjuster screw when performing swaging after the final adjustment, but requires to fix the adjuster screw by two steps, namely the temporary fixing and the final fixing. This increases man-hours for attaching the adjuster screw, which hinders improvement in productivity.